In fact, the dead layer of skin cells on your body is more than enough. External alpha radiation cannot harm you unless the concentration is truly mammoth, and it is impossible for U-238 to create such a concentration no matter how much is present.

(emphasis mine). That's true. But external sources of alpha particles are not the concern. While dead skin is pretty much impenetrable, soft lung tissue is something else entirely. And one of the main concerns about DU is that fine dust containing trace amounts can be inhaled - which means that you could end up with alpha emissions inside your lungs. This is a bad thing.

However, other instances of radiation paranoia are completely absurd, such as the fracas over radiation-sanitizing of meat. This is a sensible and completely safe method of removing harmful bacteria and other microorganisms, and if such meat ever passes the hysteria legislation stage, I will only buy meat that has been zapped. I'll never buy non-zapped meat again, given the choice.

We recently treated a 34-year-old man for Graves disease with 20 mCi of iodine 131. Twenty-four hours after treatment, his radioactive iodine uptake was 63%. Three weeks after treatment, he returned to our clinic complaining that he had been strip-searched twice at Manhattan subway stations. Police had identified him as emitting radiation and had detained him for further questioning. He returned to the clinic and requested a letter stating that he had recently been treated with radioactive iodine.

This patient's experience indicates that radiation detection devices are being installed in public places in New York City and perhaps elsewhere. Patients who have been treated with radioactive iodine or other isotopes may be identified and interrogated by the police because of the radiation they emit.

Read the article, it seems that police in New York have set up radiation detectors in the subways to try and detect potential "dirty" bombs. Without any information as to what energies their detectors are calibrated for, it's impossible to tell if they are being reasonable or not - but the fact that they picked up a patient with standard iodine treatment suggests to me that they are casting their net at the wrong end of the pool.

If anyone wants to turn to a definitive source for both the types of radiation that occur from physical decay processes, and the biological effects of these decay products, I recomend these textbooks (all of which I am using in my own medical physics studies):

These are the Bibles of the field of radiation physics and radiation therapy. I know these are expensive, but they should be in your local library. It isn't light reading, but there really needs to be better education of the public about the various types and risk of radiation, and how it's societal benefits compare to the dangers. Maybe I'll start blogging about this more, myself...